1. Field of the Invention
The present invention relates to a film formation method and apparatus for a semiconductor process for forming a silicon oxide film on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, etching, oxidation, diffusion, reformation, annealing, and natural oxide film removal. For example, where a silicon oxide film is formed on semiconductor wafers, tetraethoxysilane (TEOS: Si(OC2H5)4) may be used to perform a CVD (Chemical Vapor Deposition) process as a film formation process in a vertical heat processing apparatus (of the so-called batch type). According to this process, semiconductor wafers are first transferred from a wafer cassette onto a vertical wafer boat and supported thereon at intervals in the vertical direction. The wafer cassette can store, e.g., 25 wafers, while the wafer boat can support 30 to 150 wafers. Then, the wafer boat is loaded into a process container from below, and the process container is airtightly closed. Then, a predetermined heat process is performed, while the process conditions, such as process gas flow rate, process pressure, and process temperature, are controlled.
In recent years, owing to the demands of increased miniaturization and integration of semiconductor integrated circuits, it is required to alleviate the thermal history of semiconductor devices in manufacturing steps, thereby improving the characteristics of the devices. For vertical processing apparatuses, it is also required to improve semiconductor processing methods in accordance with the demands described above. For example, there is a CVD process which performs film formation while intermittently supplying a source gas and so forth to repeatedly form layers each having an atomic or molecular level thickness, one by one, or several by several. In general, this film formation method is called ALD (Atomic layer Deposition), which allows a predetermined process to be performed without exposing wafers to a very high temperature. Further, the ALD film formation provides good step coverage, and thus is suitable for filling recess portions of semiconductor devices, such as inter-gate gaps, which have become narrower with increased miniaturization of the devices.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-281853 (Patent Document 1) discloses a method of forming a silicon nitride film by ALD at a low temperature of 300 to 600° C. According to this method, dichlorosilane (DCS: SiH2Cl2) gas and ammonia (NH3) gas are supplied as a silane family gas and a nitriding gas, respectively, to form a silicon nitride film (SiN). Specifically, DCS gas and ammonia gas are alternately and intermittently supplied into a process container with purge periods interposed therebetween. When ammonia gas is supplied, an RF (radio frequency) is applied to generate plasma within the process container so as to promote a nitridation reaction. More specifically, when DCS gas is supplied into the process container, a layer with a thickness of one molecule or more of DCS is adsorbed onto the surface of wafers. The superfluous DCS is removed during the purge period. Then, ammonia gas is supplied and plasma is generated, thereby performing low temperature nitridation to form a silicon nitride film. These sequential steps are repeated to complete a film having a predetermined thickness.